The present invention relates to a system for receiving a transmission signal from a data carrier provided for a person, an object, or the like located in a building, a factory, or the like and for detecting the position where the person or object exists and, more particularly, to a system for detecting the position of the person or object by using spread spectrum communication.
In recent years, in association with the progress of the office automation or factory automation, it is desired to centrally manage the movements of persons or objects in a building and to properly promptly distribute information or items.
For example, in a building system which has recently been proposed, persons who enter a building possess ID cards, a managing system of the building recognizes the ID cards, thereby always grasping the locations of such persons. For instance, the managing system, can automatically transfer a received telephone call to a telephone located near a recognized person. On the other hand, in response to the use of an apparatus such as a work station or the like, the building managing system transmits a user format which is peculiar to the recognized person, thereby enabling personal use.
To realize such a building system, it is required that a communicating function such as a data carrier is provided for the ID card, a peculiar ID code is transmitted by a radio system, the transmission signal is received on the system side, and the ID code and the position are recognized.
However, a system in which ID cards (data carriers) are provided for ten thousand or more persons per building and in which ID code signals are transmitted by radio and the positions of all of the persons in the building is always recognized has not yet proposed and has not been put into practical use at present.
This is because in a radio wave propagating space such as an inner room of a building, a factory, or the like, there exists strong interferences caused by the multiple reflections of objects installed in the room and thus normal communication can not be expected using the ordinary communicating system. Also, the transmission electric power from the ID card which is used as a data carrier is extremely weak because of power source limitations and a communication quality of a high realiability cannot be obtained due to S/N ratio problems.